Impacts of Solidago gigantea on other species at home and away

Investigation of the Allelopathic Effect of Two Invasive Plant Species in Rhizotron System

A key question in plant invasion biology is why invasive plants are more competitive in their introduced habitat than in their native habitat. Studies show that invasive species exhibit allelopathy, influencing other plants by releasing chemicals. Research on allelopathy uses in vitro tests, investigating effects on seed germination and seedling development. Although soil plays a role in modifying allelopathic effects, observations with soil are rare and almost nothing is known about the root development of test plants developing in soil and the effects of allelopathic compounds on root architecture. Our study evaluates the allelopathic effects of false indigo-bush (Amorpha fruticosa L.) and common milkweed (Asclepias syriaca L.) on oilseed rape growth as a model plant. The rhizotron system was used to study the effect of morphology and root architecture. Leaf-soil mixtures at 0.5%, 1%, and 5% concentrations were used. Shoot and root development was strongly inhibited at 5%. But there was no difference between the allelopathy of the two species, and the application of lower concentrations did not show any effect, demonstrating that soil has a significant modifying effect on their allelopathy. Our results highlight that the development of roots growing in the soil is also worth investigating in connection with allelopathy, which can strengthen the ecological importance of allelochemicals during successful invasions.

Evaluation of the Effect of Organic Matter from Invasive Plants on Soil Nematode Communities

Invasive plants can cause loss of biodiversity and degradation of ecosystems with varying degrees of impact on soil communities. Little is known about how the organic matter of these invaders in the soil affects soil properties and nematode communities. We performed a pot experiment with non-invaded grassland soil and organic matter from two invasive plants, Fallopia japonica and Solidago gigantea, to assess and compare the composition and function of the nematode communities and soil properties. We tested five treatments: (1) non-invaded grassland soil (S), (2) 100% decayed organic matter from F. japonica (OMF), (3) 100% decayed organic matter from S. gigantea (OMS), (4) 50% soil plus 50% organic matter from F. japonica (S/OMF), and (5) 50% soil plus 50% organic matter from S. gigantea (S/OMS). Analysis of nematode composition was conducted over five months from May to September. The number of identified genera and diversity index was highest in the S treatment. The soil moisture content was highest, pH and the diversity index were lowest and herbivorous nematodes were absent in OMF and OMS treatments. The addition of OMF and OMS to soil decreased the soil pH and moisture content and increased the contents of organic carbon and total nitrogen. In S/OMF, the abundance of herbivores was lower than in S and the abundances of bacterivores and fungivores decreased during the study period. In the S/OMS, a significantly high diversity index was observed, similar to that in the S treatment. The selected ecological and functional indices differed between S/OMF, S/OMS and S, but not significantly. Our findings indicated that the organic matter from the two invasive plants could differentially contribute to interactions with nematode communities. A decrease in productivity and the slowing of nutrient cycling demonstrated by the decrease in the abundances of bacterivores and fungivorous nematodes may be common adding organic matter of invasive plants to soil. A decrease in the abundance of herbivores after the application of organic matter of F. japonica could potentially be used as an ecologically friendly management strategy against plant parasitic nematodes.

Effects of extracts from various parts of invasive Solidago species on the germination and growth of native grassland plant species

Allelopathy is an important factor influencing whether an invasive plant species can become successfully established in a new range through disrupting the germination and growth of native plant species. Goldenrods (Solidago species) are one of the most widespread invasive taxa in Central Europe of North American origin. Owing to their high environmental impact and wide distribution range, invasive Solidago species should be controlled in Europe, and the areas invaded by them should be restored. Numerous studies have reported the allelopathic effects of Solidago gigantea and Solidago canadensis, but the results are inconsistent regarding differences in the allelopathic effects of particular plant parts and in the sensitivity to Solidago allelopathic effects among native species as well as between the two invasive species themselves. In this study, we aimed to analyse the effect of water extracts from S. canadensis and S. gigantea parts (roots, rhizomes, stems, leaves, and inflorescences) on the germination and initial growth of seedlings of 13 grassland species that typically grow in Central Europe. The tested grassland species differed in susceptibility to Solidago allelopathy, with the most resistant species being Schedonorus pratensis, Lolium perenne, Trifolium pratense, Daucus carota and Leucanthemum vulgare. The inhibitory effect of 10% water extracts from leaves and flowers were stronger than those from rhizomes, roots, and stems without leaves, regardless of the Solidago species. Our study results imply that reducing the allelopathic effect of Solidago during habitat restoration requires removal of the aboveground parts, including fallen leaves. The allelopathic effects of roots and rhizomes seem to be of secondary importance.

Do Reproductive Traits of Invasive Populations of Scotch Broom, Cytisus scoparius (Fabaceae), Outperform Native Populations?

Reproductive traits are among the most important factors in determining the success of species establishment and invasion in a new area. Studies on transcontinental invasions have revealed that invasive species perform better in the invasive range than in their native ranges. We assumed that the same regularity exists in intracontinental invasions and thus investigated whether the reproductive traits of Scotch broom, Cytisus scoparius, perform better in the alien invasive range in Europe compared to its native range in the same continent. The aim of this research was to reveal the potential and realised fecundity of C. scoparius in its native and invasive ranges, as well as relationships with the size of pods, habitat type, and how these traits vary at the same site in different years. The results of this study were not able to unambiguously confirm our hypothesis that C. scoparius in the invasive range in Lithuania, specifically in the southern part of the Boreal biogeographical region, outperform plants in the native range with regard to the analysed reproductive traits. Potential fecundity of C. scoparius in the native range was significantly higher than in the invaded range; however, realised fecundity was not significantly different between the native and invasive ranges. The pod length was similar in both ranges, whereas the pod width was significantly greater in the invasive range than in the native range. The results suggest that the number of ovules per pod, number of matured seeds, and the size of pods are related with the type of habitat and local environmental conditions in the habitat. Although many studies on other species have confirmed higher fecundity and overall better performance of plants in the invasive range than in the native range on other continents, this rule probably cannot be applied for intracontinental invasive species occurring in relatively close geographical regions to their native ranges.

Distribution Patterns of Essential Oil Terpenes in Native and Invasive Solidago Species and Their Comparative Assessment

The importance of invasive Solidago L. species to the environment creates a new approach to controlling their spread through the use of potentially high value raw materials. The aim of this study was to assess the distribution patterns of volatile compounds in the four Solidago spp., by identifying common and species-specific compounds with their potentials, and to confirm the origin of the spontaneous hybrid Solidago × niederederi on the basis of comparative assessment of essential oil (EO) profiles. Plant material in the flowering phase was collected in mixed populations from six different sites. The EOs were isolated separately from the leaf and the inflorescence samples by hydrodistillation for 3 h. The chemical analysis was performed by gas chromatography—mass spectrometry. Multivariate data analysis was employed to explain the interspecies relationships among Solidago spp. The results revealed the similarity among Solidago spp. EO profiles, which were dominated by monoterpenes and oxygenated compound fractions. Solidago spp. differed in species distinctive terpenes and their distribution between accessions and plant parts. Volatile compound patterns confirmed the origin of Solidago × niederederi between Solidago canadensis and Solidago virgaurea, with the higher contribution of alien species than native ones. Correct taxonomic identification of species is highly essential for the targeted collection of raw material from the wild for different applications. Solidago spp. can be considered to be underutilized sources of bioactive secondary metabolites.

Inherent conflicts between reaction norm slope and plasticity indices when comparing plasticity: a conceptual framework and empirical test

Phenotypic plasticity index (PI), the slope of reaction norm (K) and relative distances plasticity index (RDPI), the most commonly used estimators, have occasionally been found to generate different plasticity rankings between groups (species, populations, cultivars or genotypes). However, no effort has been made to determine how frequent this incongruence is, and the factors that influence the occurrence of the incongruence. To address these problems, we first proposed a conceptual framework and then tested the framework (its predictions) by reanalyzing 1248 sets of published data. Our framework reveals inherent conflicts between K and PI or RDPI when comparing plasticity between two groups, and the frequency of these conflicts increases with increasing inter-group initial trait difference and/or K values of the groups compared. More importantly, the estimators also affect the magnitude of the inter-group plasticity differences even when they do not change groups' plasticity rankings. The above-mentioned effects of plasticity estimators were confirmed by our empirical test using data from the literature, and the conflicts occur in 203 (16%) of the 1248 comparisons between K and indices, indicating that a considerable proportion of the comparative conclusions on plasticity in literature are estimator-dependent. The frequency of the conflicts is influenced by phylogenetic relatedness of the groups compared, being lower when comparing within relative to between species, but not by specific types of environments, traits and species. Our study indicates that care is needed to select estimator when comparing groups' plasticity, and that the conclusions in relevant literature should be treated with great caution.

Characterization of the Habitat- and Season-Independent Increase in Fungal Biomass Induced by the Invasive Giant Goldenrod and Its Impact on the Fungivorous Nematode Community

Outside its native range, the invasive plant species giant goldenrod (Solidago gigantea) has been shown to increase belowground fungal biomass. This non-obvious effect is poorly characterized; we don’t know whether it is plant developmental stage-dependent, which fractions of the fungal community are affected, and whether it is reflected in the next trophic level. To address these questions, fungal assemblages in soil samples collected from invaded and uninvaded plots in two soil types were compared. Although using ergosterol as a marker for fungal biomass demonstrated a significant increase in fungal biomass, specific quantitative PCR (qPCR) assays did not point at a quantitative shift. MiSeq-based characterization of the belowground effects of giant goldenrod revealed a local increase of mainly Cladosporiaceae and Glomeraceae. This asymmetric boost in the fungal community was reflected in a specific shift in the fungivorous nematode community. Our findings provide insight into the potential impact of invasive plants on local fungal communities.

Chemical Composition and Antiproliferative Effect of Essential Oils of Four Solidago Species (S. canadensis, S. gigantea, S. virgaurea and S.×niederederi)

There is a growing interest in the research of natural products with potent activity in the prevention and treatment of diseases. Thereby, essential oil phytochemicals have demonstrated broad bioactivities. This study highlights the chemical composition of essential oils obtained from the leaves and inflorescences of diverse species of the genus Solidago (Solidago canadensis, Solidago gigantea, Solidago virgaurea and Solidago×niederederi), also known as Goldenrod, through GC/MS analysis, and their antiproliferative activity on three human tumor cell lines (MDA-MB 231, A375 and HCT116) by the MTT assay. The most represented chemical classes in the essential oils were oxygenated sesquiterpenes, sesquiterpene hydrocarbons, oxygenated monoterpenes and monoterpene hydrocarbons, with a remarkable contribution of compounds such as germacrene D (3.89-19.51 %), α-pinene (3.59-18.82 %), bornyl acetate (3.30-12.73 %) and caryophyllene oxide (3.07-9.18 %). Chemical quali- and quantitative differences were noticed between the leaves and flowers of the same species, as well as between the studied species. The MTT assay showed that the essential oils from the leaves were more active than those from the flower ones. The essential oil having the highest impact on cell viability was that from S.×niederederi (IC₅₀ =12.93, 6.72, and 6.82 μg/ml), followed by S. virgaurea (IC₅₀ =13.39, 7.96, and 8.36 μg/ml) and finally S. gigantea (IC₅₀ =18.04, 5.94, and 8.10 μg/ml) on MDA-MB 231, A375 and HCT116 cell lines, respectively. The essential oil from S. canadensis showed the lowest activity (IC₅₀ =29.33, 12.63, and 18.03 μg/ml, respectively). Taken together, these findings highlight the Solidago species as good sources of cytotoxic compounds. Further studies are encouraged on the in vivo effects and safety of these products.

Understanding the importance of spatial scale in the patterns of grassland invasions

The invasion of alien plant species is a serious problem for conservation and the maintenance of biodiversity in grasslands. Therefore, it is important to find environmental factors correlated with the distribution of invasive species in such areas. In this study, we examined the impacts of environmental factors operating at different spatial scales on the distribution of invasive species. The study area were located in the Sudetes Mountains, Poland (3800 km²). We sampled field data from 163 random plots located in grassland, among which there were 94 plots with invasive species and 69 plots without invasive species. For each plot, we collected data on resident vegetation (species richness, community structure), geodiversity (topography, soil type), environmental heterogeneity (landscape structure) and climate (temperature and precipitation). Since the factors examined are likely to operate at different spatial scales, we calculated values of environmental variables with different spatial scopes (10m² plot and buffers with 50, 250 and 1250 m radii). The probability of invasive plant presence was modeled using boosted regression trees (BRT). The results of our study showed that the distribution of invasive species is explained by factors operated at different spatial scale: in the finer scale the presence of invasive species was driven predominantly by the average Ellenberg's Indicator Values for soil moisture, in medium-scale by the average topographic wetness index and sum of edges, while at coarse-scale by temperature. It was also presented that the effect of drivers operating at fine-spatial scale is overwhelming by effect of drivers operating at coarse scale. From a practical point of view, the results demonstrate that effective grassland management should be planned on a larger spatial context, because focussing on the management of a single site cannot be successful.